1. Field of the Invention
The present invention relates to a tension adjusting apparatus and more particularly relates to a tension adjusting apparatus which can maintain the tension of an elongated member at a predetermined value. One end of the elongated member in its longitudinal direction and the other end are connected with each other so as to be disposed in the shape of a loop so that motive power can be transmitted thereby.
2. Description of the Related Art
Various types of motive power transmission mechanisms are well known for moving a member to be moved by transmitting motive power to the member through a loop-shaped or endless elongated member whose one end in its longitudinal direction and other end are connected with each other.
For example, with respect to a window regulator for opening and closing window glasses of a vehicle, the prior art discloses a mechanism wherein a driving source such as a motor is connected to a window glass by means of an endless wire or flexible tape. Torque of the motor is transmitted to the glass through such a wire or tape so that the window glass can be raised or lowered. Such a window regulator using a wire driving system has advantages over a well-known x-arm type window regulator in that it is lightweight, the degrees of freedom for installation thereof can be increased, and it has a wide range of applications.
However, in the above-described motive power transmission mechanism using an endless elongated member such as wire or flexible tape, it is necessary to continuously remove looseness from the endless elongated member and maintain the tension thereof at a predetermined value since the motive power cannot be transmitted properly when the endless elongated member is loose. Therefore, a mechanism for preventing looseness of an endless elongated member therefor (a tension adjusting apparatus) has been already proposed which is disclosed in U.S. Pat. No. 5,022,184 corresponding to Japanese Patent Application Laid-open No. 1-275878.
This mechanism for preventing looseness of an endless elongated member is such that a tension coil spring (tension applying member) is suspended between portions facing each other of a tape via tape guides. The spring always urges the tape in the direction in which the portions approach to each other. Thus, even if the tape is about to loosen, it is instantly stretched by means of the tension coil spring, so that the tension of the tape can be maintained at a predetermined value without generating looseness therein. As a result, this allows motive power to be reliably transmitted via the tape.
However, in the above-described mechanism for preventing looseness of an endless elongated member, a tension coil spring suspended over a tape, namely, a tape guide slides and touches the tape while the tape is moved. The frictional resistance therein is increased, thereby preventing a smooth movement of the tape. In addition, this causes wear of the tape and/or tape guide and degradation of the durability thereof.